Equivalent DB2 syntax for the Oracle DECODE function

Well, first of all, let's explain the Oracle DECODE expression for those not familiar with Oracle. A DECODE expression will look like this:

	DECODE(expr,search,result,default)

There can be multiple search values and results, and default is optional. To evaluate this expression, Oracle compares expr to each search value one by one. If expr is equal to a search, Oracle returns the corresponding result. If no match is found, Oracle returns default, or, if default is omitted, null is returned. If expr and search contain character data, Oracle compares them using nonpadded comparison semantics. The maximum number of components in the DECODE expression, including expr, searches, results, and default is 255.

So, basically, DECODE changes the value of an expression if the expression is equal to one of the values in the searched list. For example, this expression decodes the value deptno. If deptno is 10, the expression evaluates to 'ACCOUNTING'; if deptno is 20, it evaluates to 'RESEARCH'; etc. If deptno is not 10, 20, 30, or 40, the expression returns 'NONE'.

DECODE (deptno,10, 'ACCOUNTING',
20, 'RESEARCH',
30, 'SALES',
40, 'OPERATION',
'NONE')

In DB2 this can be accomplished using CASE expression. To write the equivalent of the above using DB2 you can write the following SQL statement:

SELECT CASE deptno
         WHEN 10 THEN 'ACCOUNTING'
         WHEN 20 THEN 'RESEARCH'
         WHEN 30 THEN 'SALES'
         WHEN 40 THEN 'OPERATIONS'
         ELSE 'NONE'
       END CASE
FROM EMP;

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